This invention is directed generally to the field of devices for making and breaking electrical contacts in relatively high voltage environments and more particularly to an improvement in a current carrying assembly for a circuit breaker.
While the current invention may find other uses, such as in switches, contactors, connectors, and the like, the invention will be described herein with reference to a circuit breaker for relatively high voltage applications. The specific circuit breaker described herein is of the type generally known as a hybrid ICL circuit breaker. One such circuit breaker is made by Schneider Electric/Square D Company under the designation PROXIMA(trademark) C5.
In such circuit breakers, a number of blades in a moveable pole or blade assembly are arranged to make and break contact with a fixed contact in order to close or open the circuit between the two terminals of the breaker. In order to assure good contact pressure when the breaker is closed, one or more springs are provided to compress the contacts of the moveable pole assembly against the fixed contact. Generally speaking, this has been done by using a compression spring associated with each of the multiple blades of the moveable contact or pole assembly. However, because the blades are spaced in relatively close parallel alignment, the space available for a spring relative to each blade is limited. Therefore, relatively small sized springs have been selected and used heretofore for this application. If it were possible to increase the size (volume) of the springs, more desirable spring characteristics chould be obtained, such as lower spring rate, lower stress concentration factors, and the like.
In addition, during high-level short circuits there can be a relatively large quantity of molten metal and/or plasma circulating in proximity to the blade springs. Accordingly, it is desirable to provide some protective barrier to shield the springs, at least in part, from this material under such conditions. Moreover, during high in-rush currents (up to 12 times the nominal current rating of the breaker) the temperature of the blades can exceed the recommended working temperature of the spring. Such conditions can last for several seconds. Accordingly, it is desirable to provide some means to protect the springs from heat transfer from the blades during such conditions.
Accordingly, it is a general object of the invention to provide a circuit breaker assembly having a blade spring configuration which addresses the above-noted considerations.
More specifically, it is an object of the invention to provide a breaker design in which the blade springs of larger size can be utilized in order to increase the available volume, allow for better shape in a relatively larger spring having more desirable characteristics such as lower spring rate, lower stress concentration factors, and the like. In addition, the springs, when somewhat larger are able to bend enough to provide enough independent force to each blade of the multiple blade assembly, so as to compensate for differences in wear and in manufacturing variables and tolerances commonly encountered in such assemblies.
Another object of the invention is to provide a protective device for protecting the blade springs both from materials that may be ejected during high-level short circuits, as well as from excessive heat transfer during high in-rush current conditions.
Briefly, in accordance with the foregoing, a blade assembly for use in a circuit breaker, said blade assembly comprising a plurality of blades, including one or more pairs of adjacent side-by-side blades having coplanar contact surfaces and coplanar bearing surfaces, at least one set of blade springs, each set having one end in operative contact with said bearing surface of each of a pair of adjacent side-by-side ones of said blades, said at least one set of blade springs comprising at least one compression spring.
In another embodiment of the foregoing, a blade assembly for use in a circuit breaker, said blade assembly comprising means for directing the current through a plurality of blades, including one or more pairs of adjacent side-by-side blades having coplanar contact surfaces and coplanar bearing surfaces, and means for providing a loading force on said blades using at least one set of blade springs, each having one end in operative contact with said bearing surface of each of a pair of adjacent side-by-side blades, said at least one set of blade springs comprising at least one compression spring.